Dairy products are the main food elements of the man. Milk is the sole food for infants and it plays an important role in feeding of the sick, convalescent, and healthy adults. The Yaroslavl Region is a leading region of the Yaroslavl cattle breed. Therefore, the aim of our research was to determine the strength and reliability of the influence of the factor ?genetic value of the sire? on productive characteristics of animals as a factor that helps to increase the productivity of animals. When we determine the strength of the influence of factors for statistical data we used the procedure of generalized linear models (General Linear Models - GLM), and evaluation components of phenotypic variation attributes were analyzed by multivariate dispersive analysis. Our research has allowed to allocate bulls with genetic value which has the improving effect. Using the recommended lines the farmers of the Yaroslavl region may increase productive characteristics of animals and the profit of the farms and improve the efficiency of breeding.

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The article describes a model for estimating the genotype of cattle developed and tested on actual livestock. The model is a selection index that takes into account the live weight of young animals aged 6 and 9 months. The average and high correlation between the indicators of live weight of young animals aged 6 and 9 months, lim rP 0.49…0.63 end rG 0.38…0.58. The Accuracy of genotype estimation (RJH) using the developed model is 0.57…0.66. The expected genetic improvement in live weight when using the index was 1.29…2.40 kg at the age of 6 months and 0.94…2.20 kg at the age of 9 months. The model allows for an early assessment of the breeding value of young animals aged 6-9 months at the level of short-term breeding programs for dairy cattle herds. In conjunction with the index assessment of ancestral indicators, it can be used in the formation of elite groups of young animals.

Interbreeding usage in order to improve Russian livestock in recent decades has become widespread. At the same time, an extremely high heterosis effect was established, which is demonstrated in higher productivity parametres of the cross-breeding cattle in comparison with the initial breeds. The aim of this work was to identify heterosis share effect by maternal and paternal basis factors, the blood level of the improving breed, as well as complex environmental effect of the "year of lactation" in the overall effectiveness of selection measures associated with crossbreeding. It was found that the share effect of the improving breed practically does not change for all genotypes and ranges from 0.39 to 0.44 depending on the genotype. The share effect of maternal breed is minimal in the group of animals with Holstein breed blood content of 50% and is 0.15 and it is maximum in the variants of backcrossing.